This invention is generally directed to amorphous silicon imaging members, and more specifically the present invention is directed to layered photoresponsive imaging members containing therein hydrogenated amorphous silicon, and as overcoatings certain silane or silicone compositions. In one embodiment of the present invention, there is provided a layered photoresponsive imaging member comprised of a supporting substrate, a photoconductive layer of hydrogenated amorphous silicon, and an overcoating thereof of silicone-silica hybrid components. Moreover, the aforementioned hybrid overcoatings can be selected for a variety of photoconductive imaging members containing hydrogenated amorphous silicon inclusive of those illustrated in copending applications and U.S. patents described hereinafter. The aforementioned imaging members of the present invention can be incorporated into electrophotographic; and in particular xerographic imaging and printing systems wherein, for example, the latent electrostatic patterns which are formed can be developed into images of high quality and excellent resolution at substantially all humidity values inclusive of those situations wherein the relative humidity is greater than 70 percent. Many of the prior art photoresponsive imaging members containing hydrogenated amorphous silicon are sensitive to relative humidities, particularly in excess of 50 percent, thus the resolution image loss can be substantial, for example, at relative humidities of greater than 70 percent as illustrated hereinafter, the resolution loss is substantially greater than 90 percent rendering the resulting images unusable and unreadable. Accordingly, the photoresponsive imaging members of the present invention when incorporated into electrostatographic imaging systems are of substantial assistance in eliminating and/or preventing moisture sensitivity, which will cause undesirable fuzzy images to be formulated; and further results in image deletion.
Numerous photoconductive components are known inclusive of amorphous selenium, alloys of selenium such as selenium arsenic, and the like. Additionally, there can be selected as photoresponsive imaging members various organic photoconductive materials including, for example, complexes of trinitrofluorenone and polyvinylcarbazole. Further, organic photoresponsive devices with aryl amine hole transporting molecules, and photogenerating layers inclusive of trigonal selenium are illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
Also known are amorphous silicon photoconductors, reference for example U.S. Pat. Nos. 4,265,991 and 4,225,222. There is disclosed in the '991 patent an electrophotographic photosensitive member comprised of a substrate, and a photoconductive overlayer with a thickness of 5 to 80 microns of amorphous silicon containing 10 to 40 atomic percent of hydrogen. Additionally, this patent describes several processes for preparing amorphous silicon. In one process embodiment, there is prepared an electrophotographic photosensitive member by heating the member present in a chamber to a temperature of 50.degree. C. to 350.degree. C., introducing a gas with silicon and hydrogen atoms, providing an electrical discharge in the chamber by electric energy to ionize the gas, followed by depositing amorphous silicon on an electrophotographic substrate at a rate of 0.5 to 100 Angstroms per second by utilizing an electric discharge thereby resulting in an amorphous silicon photoconductive layer of a predetermined thickness. Although the amorphous silicon device described in this patent is photosensitive, after a minimum number of imaging cycles, less than about 1,000 for example, unacceptable low quality images of poor resolution with many deletions may result. With further cycling, that is subsequent to 1,000 imaging cycles and after 10,000 imaging cycles, the image quality may continue to deteriorate often until images are partially deleted.
Further, there is disclosed in the prior art amorphous silicon photoreceptor imaging members containing, for example, stoichiometric silicon nitride overcoatings; however, these members in some instances generate prints of low resolution as a result of the band bending phenomena. Additionally, with the aforementioned silicon nitride overcoatings, the resolution loss can in many instances be extreme thereby preventing, for example, any image formation whatsoever.
There are also illustrated in copending applications photoconductive imaging members comprised of amorphous silicon. Accordingly, for example, there is illustrated in copending application U.S. Ser. No. 695,990, entitled Electrophotographic Devices Containing Compensated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, an imaging member comprised of a supporting substrate and an amorphous hydrogenated silicon composition containing from about 25 parts per million by weight to about 1 percent by weight of boron compensated with substantially equal amounts of phosphorous. Furthermore, described in U.S. Pat. No. 4,544,617, entitled Electrophotographic Devices Containing Overcoated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of a supporting substrate, an amorphous silicon layer, a trapping layer comprised of doped amorphous silicon, and a top overcoating layer of stoichiometric silicon nitrides. More specifically, there is disclosed in this patent an imaging member comprised of a supporting substrate; a carrier transport layer comprised of uncompensated or undoped amorphous silicon; or amorphous silicon slightly doped with p or n type dopant such as boron or phosphorous; a thin trapping layer comprised of amorphous silicon which is heavily doped with p or n type dopants such as boron or phosphorous; and a top overcoating layer of specific stoichiometric silicon nitride, silicon carbide, or amorphous carbon. However, one disadvantage associated with the aforementioned imaging member is that the trapping layer introduces a dark decay component which reduces the charge acceptance for the imaging member.
Additionally, described in U.S. Pat. No. 4,613,556, entitled Heterogeneous Electrophotograhic Imaging Members of Amorphous Silicon, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of hydrogenated amorphous silicon photogenerating compositions, and a charge transporting layer of plasma deposited silicon oxide.
Other representative prior art disclosing amorphous silicon imaging members, including those with overcoatings, are U.S. Pat. Nos. 4,460,669; 4,465,750; 4,394,426; 4,394,425; 4,409,308; 4,414,319; 4,443,529; 4,452,874; 4,452,875; 4,483,911; 4,359,512; 4,403,026; 4,416,962; 4,423,133; 4,460,670; 4,461,820; 4,484,809; and 4,490,453. Additionally, patents that may be of background interest with respect to amorphous silicon photoreceptor members include, for example, U.S. Pat. Nos. 4,359,512; 4,377,628; 4,420,546; 4,471,042; 4,477,549; 4,486,521; and 4,490,454.
Further, additional respresentative prior art patents that disclose amorphous silicon imaging members include, for example, U.S. Pat. No. 4,357,179 directed to methods for preparing imaging members containing high density amorphous silicon or germanium; U.S. Pat. No. 4,237,501 which discloses a method for preparing hydrogenated amorphous silicon wherein ammonia is introduced into a reaction chamber; U.S. Pat. Nos. 4,359,514; 4,404,076; 4,403,026; 4,397,933; 4,423,133; 4,461,819, 4,237,151; 4,356,246; 4,361,638; 4,365,013; 3,160,521; 3,160,522; 3,496,037; 4,394,426; and 3,892,650. Of specific interest are the amorphous silicon photoreceptors illustrated in U.S. Pat. Nos. 4,394,425; 4,394,426 and 4,409,308 wherein overcoatings such as silicon nitride and silicon carbide are selected. Examples of silicon nitride overcoatings include those with a nitrogen content of from about 43 to about 60 atomic percent.
Moreover, the use of silicones and reactive silane coupling agents as overcoatings for photoreceptors, excluding amorphous silicon imaging members, is illustrated in U.S. Pat. Nos. 4,148,637; 4,256,823; 4,371,600, the disclosures of which are totally incorporated herein by reference; and U.S. Pat. Nos. 4,407,920 and 4,439,509, the disclosures of which are totally incorporated herein by reference. Other patents of background interest with respect to amorphous silicon photoreceptors are U.S. Pat. Nos. 4,529,679 and 4,536,459.
With some of the aforementioned hydrogenated amorhous silicon photoconductive members, particularly those containing overcoatings, for example, of silicon nitride and silicon carbide, the resulting members are not free of chemical and environmental stabilities. For example, although these devices may be useful for their intended purposes at certain relative humidities, for example when this humidity exceeds greater than 70 percent,image deletion believed caused by surface conductivity occurs. Although it is not desired to be limited by theory, it is believed that this is caused by corona ions that induce chemical changes on the surface of the silicon nitride or other equivalent overcoatings. Therefore, in the presence of sufficient water molecules, for example greater than 70 percent relative humidity, surface conductivity is enhanced permitting undesirable resolution loss and image deletion. With the imaging members of the present invention, this problem of humidity sensitivity is alleviated. Therefore, there is a need for hydrogenated amorphous silicon photoresponsive imaging members with improved characteristics. Specifically, there is a need for layered hydrogenated silicon imaging members that possess desirable high charge acceptance value, low charge loss characteristics in the dark, and further are insensitive to humidity. Furthermore, there continues to be a need for layered photoresponsive imaging members with a first overcoating layer of silicon nitride or silicon carbide, and thereover an overcoating layer of a silicon or silicone compound thereby enabling the substantial elimination of image deletion at high relative humidities. Furthermore, there is a need for improved layered hydrogenated amorphous silicon imaging members enabling images of increased resolution, no smudging, when compared to similar members containing therein only a single overcoating of a silicon nitride. Additionally, there is a need for improved layered imaging members with a top overcoating layer of a silicon or silicone-silica hybrid component, which members permit photoconductors with humidity insensitivity, and are not adversely effected by electrical consequences resulting from scratching and abrasion. There is also a need for hydrogenated amorphous silicon imaging members which can be selected for use in repetitive imaging and printing systems. Furthermore, there is a need for amorphous silicon imaging members with low surface potential decay rates in the dark, and photosensitivity in the visible and near visible wavelength range. In addition, there is a need for improved layered amorphous silicon imaging members which have very few image defects such as white spots